Nickel/alumina catalyst

ABSTRACT

The invention provides a nickel/alumina catalyst, with an atomic ratio of nickel/aluminum between 10 and 2, an active nickel surface area between 70 and 150 m 2  /g nickel and an average pore size, depending on the above atomic ratio, between 4 and 20 nanometers. Preferably the nickel/aluminum atomic ratio is between 10 and 4. Preferably the catalyst has a specific porous structure. 
     The invention also provides a method for preparing the catalyst by a two step process involving precipitating nickel ions and adding during a second, so-called aging step a soluble aluminum compound. 
     The catalyst is useful for hydrogenating unsaturated organic compounds in particular oils.

This is a continuation of U.S. application Ser. No. 747,440 filed June21, 1985, now U.S. Pat. No. 4,657,889.

The application relates to a hydrogenation catalyst containing nickeland alumina, as well as to the preparation and use thereof.

Catalysts containing nickel/alumina are known and are mainly applied forthe preparation of methane-containing gas. It is usual to prepare suchcatalysts by co-precipitating nickel- and alumium ions from a solutionwith an alkaline reagent like, e.g., ammonium carbonate as is disclosedin U.S. Pat. No. 3,320,182 (Esso Research).

According to this co-precipitation method, catalysts are obtained whichhave reasonably good properties, but the filterability of the catalystprecursor (green cake) and catalytic properties, particularly in thehydrogenation of unsaturated triglyceride oils, are inadequate. The BETtotal surface area of these catalysts is typically below 200 m² /g ofcatalyst and the average pore size is in the order of a few nanometers.

The present invention provides novel nickel/alumina catalysts which haveconsiderably improved properties and which have an atomic ratio ofnickel/aluminium between 10 and 2, the active nickel surface area isbetween 70 and 150 m² /g nickel and the average pore size, depending onthe above atomic ratio, is between 4 and 20 nanometers.

Preferably the atomic ratio of nickel to aluminium of these catalysts isbetween 10 and 4 because this results in a higher hydrogenationselectivity of the catalyst i.e. less formation of completely saturatedtriglycerides which is probably due to a higher average mesopore size.

Further these catalysts preferably have an open, porous structure withmacropores of 100-500 nanometers and mesopores having an average sizebetween 8 and 20 nanometers. As is apparent from electronmicroscopy themacropores are formed by interconnected catalyst platelets.

As a rule, these catalysts have an active nickel surface area between 90and 150 m² /g of nickel. The BET total surface area is usually between90 and 450 m² /g of catalyst. The average diameter of the nickelcrystallites is preferably between 1 and 5 nanometers.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE (FIG. 1) is an electron micrograph of a catalyst according tothe invention.

The above-mentioned improved catalysts can be advantageously prepared bya process in which an insoluble nickel compound is precipitated from anaqueous solution of a nickel salt with an excess alkaline precipitatingagent, which precipitate is subsequently allowed to age in suspendedform and is then collected, dried and reduced, wherein, after the nickelions have been precipitated, a soluble aluminium compound is added. Thesoluble aluminium compound can be added as a solution but also asundissolved crystals. The soluble aluminium compound being added afterthe nickel ions have been substantially precipitated is e.g. aluminiumnitrate, sodium aluminate or alumina which dissolves at least partly inthe excess alkali.

After precipitation and ageing according to the invention, theprecipitate is separated from the liquid, usually washed, dried andactivated with hydrogen at an elevated temperature, this by usualprocedures.

Nickel compounds which can be used as starting material for thecatalysts according to this invention are water-soluble nickel compoundssuch as nitrate, sulphate, acetate, chloride and formate. The solutionswhich are charged to the precipitation reactor preferably containbetween 10 and 80 g nickel per liter; especially preferred are solutionswhich contain between 25 and 60 g nickel per liter.

Alkaline precipitation agents which can be used as starting material forthe catalysts according to the present invention are alkali metalhydroxides, alkali metal carbonate, alkali metal bicarbonate, thecorresponding ammonium compounds and mixtures of the above-mentionedcompounds. The concentration of the alkaline solution which is fed intothe precipitation reactor is preferably between 20 and 300 g alkalinematerial (calculated as anhydrous material) per liter (in as far as thesolubility allows this), more particularly between 50 and 250 g perliter.

It is convenient to use both solutions (of metal salt and alkalinecompound) in almost the same concentrations (expressed in equivalents),so that approximately the same volumes can be reacted.

The metal-containing solution and the alkaline solution are added insuch amounts per unit of time that a small excess of alkaline compoundis present during the precipitation step, so that the normality of theliquid is between 0.05 and 0.5, preferably between 0.1 and 0.3 (thisnormality is determined by titrating a solution of hydrochloric acid,with methyl-orange as indicator). Sometimes it is necessary to add somemore alkaline solution during the ageing step, in order to keep thenormality within the range indicated above.

The precipitation reactor has such dimensions with respect to theamounts of liquid pumped in, that short average residence times can beobtained. As a rule, average residence times of between 0.1 sec. and 10minutes, preferably between 0.2 sec. and 4.5 minutes are used in theprecipitation reactor.

In a preferred embodiment, in which the precipitation step (step 1) iscarried out continuously, the amounts of solutions fed into theprecipitation reactor are controlled by measuring, optionallycontinuously, the normality or pH of the reactor effluent. Thetemperature at which the precipitation takes place can be controlled byadjusting the temperatures of the liquids fed in. The required vigorousagitation of the liquid in the precipitation reactor preferably takesplace with a mechanical energy input of between 5 and 2000 watts per kgof solution. More preferably the agitation takes place with a mechanicalenergy input of 100 to 2000 watts per kg of solution.

The reaction mixture obtained from the precipitation reactor goesimmediately thereafter to a stirred post-reactor of a significantlyhigher capacity in which the suspension is agitated and aged. At thisstage soluble aluminium compounds and possible other compounds areadded, and optionally carrier material and promotors if any. The amountof aluminium compound added is 0.1 to 0.5, preferably 0.1 to 0.25 molaluminium ions per gram atom of nickel in the suspension. Preferably, asoluble compound such as aluminium nitrate or sodium aluminate is added.Preferably the liquid in the ageing reactor, thus during the ageingstep, is kept at a temperature between 40° and 100° C., preferablybetween 60° and 98° C.

The precipitation step and also the maturing step can be carried outbatchwise (=discontinuously), continuously and semi-continuously (e.g.according to the cascade method).

Usually the normality of the liquid in the ageing-reactor during theageing step (step 2) is kept in the same range as during theprecipitation step (step 1); if necessary by adding some more alkali.The ageing step can be carried out in one or more reactors, the (total)average residence time being maintained between 20 and 180 minutes,preferably between 30 and 150 minutes. If two or more reactors are used,it is preferred to have the temperature in the second or further reactor5 to 15 centigrades lower than in the preceding ageing reactor.

After the ageing step has been completed, the solid material isseparated from the mother liquor, usually washed, dried, optionallyground and calcined and thereafter activated with hydrogen at antemperature, between 250 and 600, preferably between 350° and 500° C.This activation can take place at atmospheric pressure or at increasedpressure.

The present process involving separate precipitation and ageing stepsresults in a catalyst precursor/green cakes which has a considerablyimproved filteratively than a co-precipitated precursor at least a fourfold improvement. Preferably before drying, or during a step precedingthat, promoters can be added. Suitable amounts of promotors are from 0.5to 10%, calculated on the weight of nickel, of elements such asmolybdenum, cobalt, copper, iron, lanthanum, magnesium, or otherelements and combinations thereof.

The solid material is preferably washed with water; sometimes somealkaline material or a surface active material is added to the washingwater. Also an organic solvents e.g. acetone can be advantageously usedduring washing. Drying preferably takes place with hot air. Spray-dryingis preferred but freeze-drying is also quite possible.

The catalyst thus obtained is especially suitable for the hydrogenationof unsaturated organic compounds particularly oils, fats, fatty acidsand fatty acid derivatives like nitriles. This hydrogenation is carriedout with hydrogen at an increased temperature (80°-250° C.) andoptionally an increased pressure (0.1-5.0 10⁶ Pa).

The hydrogenated products thus obtained, e.g. hydrogenated oils, showfavourable properties such as low tri-saturated content, sometimescombined with a steep dilatation curve.

The invention is illustrated by the following examples:

EXAMPLE 1

Solutions of Ni(NO₃)₂ (35 g Ni per liter) and Na₂ CO₃ anh. (100 g/l)were continuously pumped at equal flow rates into a vigorously stirredprecipitation reactor, where nickel hydroxide/carbonate was precipitatedat a temperature of 20° C. The pH of the suspension in this reactor was9.4. In this precipitation reactor (volume 25 ml), the suspension had anaverage residence time of 0.5 min. The suspension was then transferredcontinuously to a second, ageing reactor (volume 1500 ml), in which theaverage residence time was 30 min. and the temperature was 97° C.Simultaneously, an amount of aluminium ions was continuously dosed intothis reactor, as an aqueous solution of aluminium nitrate, at a rate of0.13 g aluminium per min. The average Al/Ni atomic ratio was 0.3.

The pH of the suspension in the second reactor was 9.0. The volume ofthe liquid in the second reactor was kept constant. In Table I this istabulated.

The ageing step was terminated after 90 min. (3× the average residencetime), and the suspension in the reactor filtered. The green filter cakethus obtained was washed with distilled water. The washed cake was: (A)dried at 120° C. in a drying oven; (B) spray dried; (C) washed withacetone and dried at room temperature. Thereafter the catalyst wasactivated for 30 minutes with hydrogen at a temperature of 400° C. Fromthe determination of the nickel surface area by hydrogen chemiabsorptionan average nickel crystallite size of 2.0 nanometers was calculated.

The filterability of the green cake was determined as follows:

1 liter of a green cake aqueous suspension with 4% (w.w.) solids fromthe ageing reactor was filtered over a Buchner funnel with a Schleicherand Schull (trade name) black band filter with a diameter of 125 mm. Thevacuum applied was 3-4,000 Pa, and obtained with an aspirator. The timeof filtration in minutes necessary for filtering 4 liters of distiledwater over the bed of green cake obtained was taken as a yardstick ofthe filterability of the green cake. This time of filtration isindicated i.a. in Table I.

The activity of the catalyst in the hydrogenation of fish oil (iodinevalue 165) was determined as follows:

150 g fish oil was hydrogenated at 180° C. and a hydrogen pressure of1.10⁵ Pa with 0.07% (w.w.) of catalyst. The decrease in the refractiveindex of the fish oil was compared with the decrease obtained in asimilar hydrogenation with a known standard catalyst and the activitywas expressed as a percentage of the activity of the standard catalyst.

As to the selectivity of the catalyst: 250 g fish oil (iodine value 165)were hydrogenated to an iodine value of 85 with 0.1% (w.w.) catalyst and60 liters H₂ /hour at a pressure of 1.10⁵ Pa at 180° C. The meltingpoint of the hydrogenated oil was determined and the time required toreach an iodine value of 85. Together they are a yardstick for theselectivity.

The oil filtration of the catalyst was determined as follows:

After the hydrogenation the suspension, i.e. the hydrogenated oilcontaining the catalyst, was cooled to 90° C. and pumped to a closed,double-walled filtration vessel which was connected to a thermostat at90° C. The bottom of this vessel contained a cotton filter cloth of 30cm diameter. After pumping the oil and the catalyst into the filtrationvessel an overpressure of 3.10⁵ Pa. was applied. During the filtrationthis pressure was maintained with a Kendall pressure regulator. Afterincreasing the pressure to 3.10⁵ Pa (t=o) the time of filtration timewas measured. The weight of the filtered oil was determined as afunction of time. Subsequently, the weight of the filtered oil (x-axis)was plotted graphically against the filtration time divided by therelevant weight of the oil (y-axis). The slope of the line obtained wastaken as a yardstick for the filter resistance of the cake. These valuesare indicated in Table II for 150 g oil in min./g.

EXAMPLES 2 AND 3

In accordance with the procedure described in Example 1, more catalystsaccording to the invention were prepared, variations being made,however, in the amounts of starting materials and conditions, asindicated in Table I below. The properties of these catalysts aresummarized in Table II.

It is noteworthy that, on an average, short hydrogenation times could beused and the catalyst retained its activity for a prolonged period whencompared with a co-precipitated catalyst. An excellent selectivity wasalso observed, i.e. there was less tri-saturated triglyceride formedespecially in the hydrogenation of soya bean oil. Further, the meltingpoint of the hydrogenated oils appeared to be practically independent ofthe atomic ratio of Al to Ni and of the conditions of washing anddrying. Finally, also the filtration properties of green cake andcatalyst after hydrogenation were particularly favourable.

EXAMPLES 4, 5 AND 6

The procedure followed was identical to that of Example 1. In this casesolutions of NiSO₄ (35 g/l Ni) and Na₂ CO₃ anh•(100 g/l) were broughttogether at equal flow rates (32 ml/min.⁻¹) at 20° C. The pH of thesuspension in the precipitation reactor was 9.4. This suspension wassubsequently transferred continuously to a second, ageing reactor(volume 1920 ml). Simultaneously, an amount of aluminium ions was dosedcontinuously into this second reactor. In the case of Example 4 anaqueous sodium aluminate was dosed (0.068 g Al/min.) whereas in the caseof Examples 5 and 6 a solution of aluminium oxide in 4N aqueous sodiumhydroxide was dosed (0.13 g Al/min.) FIG. 1 which is an electronmicrograph of the catalyst of Example 6 at a magnification of 10⁴ showsthe open spongy structure with the interconnected catalyst plateletsforming the macropores. The catalyst preparation is summarized in TableIII and the properties in Table IV.

COMPARATIVE EXPERIMENTS 1-2

The preparation was carried out according to Example I. In this case asolution of aluminium nitrate in water was dosed into the precipitationreactor.

The results are tabulated in Tables V and VI.

EXAMPLE 7

Herein the hydrogenation of C18-nitrile to amine is described. Thecatalyst was prepared according to Example 2. The reaction was carriedout in an autoclave of 200 ml, charged with 70 ml nitrile (acid value0.2) and amount of catalyst corresponding with 0.12% Ni at a hydrogenpressure of 2.5 10⁶ Pa.

The temperature was 110° C. at the start of the reaction and increasedto 120° C. due to the heat of reaction and maintained for 2.5 hours.

The ratio H₂ :NH₃ was 1:1. The conversion of the nitrile was 92%. Theyield of primary amine was 91% and the selectivity for primary amine99%.

The selectivity and rate of filtration of the spent catalyst were higherthan those which were obtained after hydrogenation with the catalystaccording to comparative experiment 2.

EXAMPLE 8

The catalyst prepared according to example 6 was tested in thehydrogenation of soybean oil. In a so-called loop jet reactor soybeanoil (IV 132) was hydrogenated using 0.02% (w.w) of Ni, at a hydrogenpressure of 6.10⁵ Pa and a temperature of 110° C. The reaction rates ofthe hydrogenation obtained with various amounts of said catalyst showedthis catalyst to be more active than a commercially availablenickel-on-guhr catalyst at equal nickel levels. Moreover, theselectivity of the reaction using said catalyst (i.e. low saturated C₁₈content (C_(18:0)) and low solid fat contents at 30° C. at an IV of 90(N₃₀)) was excellent compared to values obtained with known Ni-on-guhrcatalysts as is shown in Table VII.

EXAMPLE 9

The same catalyst as used in example 8 was tested in the hydrogenationof rapeseed oil (IV 117.5). In a so-called BUSS reactor rapeseed oil washydrogenated using 0.05% (w.w.) Ni at a hydrogen pressure of 4.10⁵ Paand a temperature of 175° C. A high selectivity with respect to C_(18:0)content and N₃₀ values was obtained with said catalyst compared with thetwo Ni-on-guhr catalysts. (N₃₀ values: 1.5% and 3.3% respectively andC_(18:0) : 10.0% and 11.5% respectively).

                  TABLE I                                                         ______________________________________                                        Example          1         2        3                                         ______________________________________                                        Ni/Al atomic ratio                                                                             3.33      10.0     2.0                                       Molarity         1.0       1.0      1.0                                       of the soda solution                                                          Molarity of the nickel                                                                         0.6       0.6      0.6                                       solution                                                                      Precipitation temperature                                                                      20        20       20                                        (°C.)                                                                  Average precipitation                                                                          0.5       0.5      0.5                                       time (min.)                                                                   pH value         9.4       9.4      9.4                                       Ageing temperature (°C.)                                                                97        97       97                                        Average ageing time (min.)                                                                     30        30       30                                        pH value         9.0       9.0      9.0                                       Filterability of green                                                                         3         1        4                                         cake (min.)                                                                   ______________________________________                                        Properties of the catalyst                                                                     A      B      A   B    A   B                                 ______________________________________                                        Active Ni surface area                                                                         115    139    95  100  95  120                               (m.sup.2 /g Ni)                                                               Ni crystallite size (nm)                                                                       1.7    2.3    4.0 1.5  4.0 2.8                               ______________________________________                                        Average pore size (nm)                                                                         6         16       5.5                                       BET-total surface area                                                                         320       180      320                                       (m.sup.2 /g catalyst)                                                         ______________________________________                                         A = washed with water                                                         B = washed with acetone                                                  

                  TABLE II                                                        ______________________________________                                        Example           1        2        3                                         ______________________________________                                        Ni % in the reduced catalyst                                                                    85       90       75                                        Fish oil activity after                                                                         98       90       45                                        washing with water (%)                                                        Fish oil activity after                                                                         150      128      120                                       spray-drying (%)                                                              Fish oil activity after                                                                         154      133      132                                       washing with acetone (%)                                                      Selectivity:                                                                  Hydrogenation time (min.)                                                     Water drying      198      220      330                                       Spray-drying      100      120      130                                       Acetone drying    84       84       84                                        Melting point (°C.)                                                    Water drying      32.0     32.5     32.0                                      Spray-drying      32.0     33.0     33.0                                      Acetone drying    31.5     32.0     32.0                                      Oil filtration after hydro-                                                   genating 150 g oil (min · g.sup.-1)                                  Water drying      0.1      0.1      0.1                                       Spray-drying      0.2      0.2      0.2                                       Acetone drying    0.25     0.25     0.2                                       ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        Example         4        5         6                                          ______________________________________                                        Ni/Al atomic ratio                                                                            10       6         5                                          Molarity of the soda                                                                          1.0      1.0       1.0                                        solution                                                                      Molarity of the nickel                                                                        0.6      0.6       0.6                                        solution                                                                      Precipitation temperature                                                                     20       20        20                                         (°C.)                                                                  Average precipitation                                                                         0.5      0.5       0.5                                        time (min.)                                                                   pH value        9.4      9.4       9.4                                        Ageing temperature (°C.)                                                               98       98        98                                         Average ageing time (min.)                                                                    30       30        30                                         pH value        9.7      9.3       9.4                                        Filterability of green cake                                                                   2.5      2         2                                          (min.)                                                                        ______________________________________                                        Properties of the catalyst                                                                    A     B      A    B    A    B                                 ______________________________________                                        Active Ni surface area                                                                        60    100    110  140  110  140                               (m.sup.2 /g Ni)                                                               Ni crystallite size (nm)                                                                      4.0   1.5    2.3  2.0  2.3  2.0                               ______________________________________                                        Average pore size (nm)                                                                        16       11        11                                         BET-total surface area                                                                        180      250       250                                        (m.sup.2 /g catalyst)                                                         ______________________________________                                         A = washed with water                                                         B = washed with acetone                                                  

                  TABLE IV                                                        ______________________________________                                        Example           4        5        6                                         ______________________________________                                        Ni % in the reduced catalyst                                                                    85       85       85                                        Fish oil activity after                                                                         100      100      110                                       washing with water (%)                                                        Fish oil activity after                                                                         125      140      150                                       spray-drying (%)                                                              Selectivity:                                                                  Hydrogenation time (min.)                                                     Water drying      200      150      120                                       Spray-drying      130      97       80                                        Melting point (°C.)                                                                      32.0     33.0     33.0                                      Spray-drying                                                                  Oil filtration after hydro-                                                   genating 150 g oil (min · g.sup.-1)                                  Water drying      0.12                                                        Spray-drying      0.18                                                        ______________________________________                                    

                  TABLE V                                                         ______________________________________                                        Comparative experiment                                                                           1          2                                               ______________________________________                                        Ni/Al atomic ratio 5          5                                               Molarity of the soda solution                                                                    1.0        1.0                                             Molarity of the nickel solution                                                                  0.6        0.6                                             Precipitation temperature (°C.)                                                           20         20                                              Average precipitation time (min.)                                                                0.5        0.5                                             pH value           9.4        9.4                                             Ageing temperature (°C.)                                                                  97         97                                              Average ageing time (min.)                                                                       30         30                                              pH value           11.0       9.4                                             Filterability of green cake                                                                      32         32                                              (min.)                                                                        ______________________________________                                        Properties of the catalyst                                                                       A      B       A    B                                      ______________________________________                                        Active Ni surface area                                                                           70     125     70   135                                    (m.sup.2 /g Ni.sup.-1)                                                        Ni crystallite size (nm)                                                                         3.0    1.6     3.6  1.6                                    ______________________________________                                        Average pore size (nm)                                                                           5          5                                               BET-total surface area                                                                           380        380                                             (m.sup.2 /g catalyst)                                                         ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                        Comparative experiment                                                                             1       2                                                ______________________________________                                        Ni % in the reduced catalyst                                                                       85      85                                               Melting point (°C.)                                                                         31.0    32.0                                             Hydrogenation time (min.)                                                                          150     120                                              Spray drying                                                                  Oil filtration after 0.17    0.17                                             hydrogenating 150 g oil                                                       (min · g.sup.-1)                                                     Spray-drying                                                                  Fish oil activity    110     110                                              Spray-drying (%)                                                              ______________________________________                                    

                  TABLE VII                                                       ______________________________________                                                   Hydrogenation rate                                                 Catalyst   (IV decrease/min.)                                                                          C.sub.18:0 (%)                                                                          N.sub.30 (%)                               ______________________________________                                        Example 6  2.2           8.2       0.7                                        Ni--on-guhr-1                                                                            1.8           10.5      4.3                                        Ni--on-guhr-2                                                                            1.7           9.5       3.2                                        ______________________________________                                    

I claim:
 1. A nickel alumina catalyst wherein the atomic ratio ofnickel/aluminum is between 10 and 2, the active nickel surface area isbetween 90 and 150 m² /g nickel, the average pore size, depending on theabove atomic ratio, is between 4 and 20 nanometers and the nickelcrystallites have an average diameter between 1 and 5 nanometers.
 2. Acatalyst according to claim 1, wherein the atomic ratio is between 10and
 4. 3. A catalyst according to claim 1, wherein the BET total surfacearea is between 90 and 450 m² /g catalyst.
 4. A catalyst according toclaim 1, wherein the catalyst has an open, porous structure withmacropores of 100-500 nanometers and a mesopore structure having anaverage pore size between 8 and 20 nanometers.
 5. A catalyst accordingto claim 4 wherein the macropores are formed by interconnected catalystplatelets.